This invention relates to improved method of producing waterproof leathers and skins.
There are in particular three methods for producing waterproof leathers and skins, namely:
(1) impregnating through the incorporation of water-insoluble substances, for example solid fats, waxes or special polymers. PA1 (2) impregnation through the incorporation of substances which swell in water and which, on taking up water, form highly viscous emulsions, blocking the interstices between the leather fibers, for example special emulsifiers of the the W/O-type. PA1 (3) treatment with hydrophobizing substances, for example aluminum and chromium complexes, silicones or organic fluoro-compounds.
A combination of methods (2) and (3) has been successfully applied in practice preferably being carried out in an aqueous liquor in a tumbler. The W/O emulsifiers are converted into hydrophobizing metal complex salts by fixing with chromium or aluminum salts after stuffing. Unfortunately, this process is attended by disadvantages insofar as the stuffing requires relatively high pH-values (above 6) to avoid surface accumulation of the fats and, hence, smearing. However, this easily leads to a certain looseness of grain of the leather. In addition, the penetrometer values obtained in practice frequently show very considerable fluctuations so that the leather may have to be aftertreated by casting, spraying or oozing.
In addition, German Published Patent Application No. F 10 300.28a, 9 describes a process for improving the properties of leather, particularly in regard to its uptake of and permeability to water, which is characterized in that aqueous solutions or emulsions of salts of carboxyl-group-containing polymers are introduced into the material, optionally in the presence of stuffing and thickening agents and/or buffer substances, and the material is optionally subjected to an aftertreatment to render the polymers insoluble. The carboxyl-containing polymers mentioned include inter alia copolymers of acrylic acid or methacrylic acid and esters thereof, the content of carboxyl-containing components varying between 2.5% and 50%. However, it was found that very large quantities of polymers (&gt;30%, based on the shaved weight of the leather) have to be incorporated to obtain as adequate impregnating effect.